In 1963, a man in Turkey uncovered a mysterious room behind the wall of his home. To his surprise, this discovery led to something much, much larger. It turns out this room was the beginning of a secret underground passageway.

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Here's the passageway he discovered: 

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These secret passageways were all interconnected and formed an entire underground city, known as Derinkuyu. 

One cannot describe how elaborate and intricate these passageways actually were. Back in the day, this underground city was a place where citizens could seek refuge away from war. It could house up to 20,000 people and had a number of unexpected amenities, including stables, chapels, and even a school! 

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Most of the entrances into this underground stone city were completely hidden. Here's a photo of one of the heavy stone doors, weighing over 1000 lbs (500 kg).

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For a long period of time in history, in between wars, these tunnels were abandoned, and they could have been forgotten forever if it wasn't for the Turkish man's discovery in 1963. Since 1969, part of the city has been open to tourists. It's crazy to realize that this was a man-made creation and even crazier to think it could have been lost for good! What other accidental discoveries have we made that perhaps could otherwise have been lost?